Prader-Willi syndrome is a major neuro-behavioral disorder occurring in about 1 out of 25,000 births. Most cases are associated with de novo cytogenetic deletions of the 15q11-13 region on the paternal chromosome or with maternal uniparental disomy leading to loss of expression of a cluster of paternally expressed genes in this region. However, there is a subgroup of PWS patients who have normal chromosomes of biparental origin but have microdeletions just upstream of the SNRPN gene; suggesting the presence of's cis-acting control sequence (an imprinting center) in this region that regulates transcription of all paternally expressed genes. The objective of this proposal is to better understand the mechanism of the role played by this imprinting center in PWS.